This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-246912, filed Aug. 16, 2000, the entire contents of which are incorporated herein by reference.
This invention relates to a method of manufacturing a synthesis gas to be employed for the synthesis of gasoline, methanol or dimethyl ether by way of the GTL (Gas to Liquid) process.
A synthesis gas comprising hydrogen (H2) and carbon monoxide (CO) is employed as a raw material for the synthesis of gasoline, etc. by way of a GTL (Gas to Liquid) process according to the Fisher-Tropsch reaction system.
This synthesis gas has been conventionally manufactured by the following method.
Namely, by making use of a synthesis gas plant provided with a reformer comprising a steam reforming reaction tube, a combustion radiation portion disposed around the reaction tube for heating the reaction tube through the combustion of fuel, and a convection portion communicated with the combustion radiation portion, steam and carbon dioxide are added to a natural gas employed as a raw gas to prepare a mixed gas, which is then passed through the convection portion so as to be preheated to a predetermined temperature. The resultant preheated mixed gas is then fed to the reaction tube so as to steam-reform the natural gas together with carbon dioxide, thereby manufacturing the synthesis gas containing hydrogen (H2) and carbon monoxide (CO). Since the temperature of the reaction tube to be heated by the combustion radiation portion can be reduced due to the preheating of this mixed gas, this preheating would contribute to a reduction of the fuel consumption.
However, if the natural gas incorporated with steam and carbon dioxide is preheated to a temperature of 550 to 600xc2x0 C. or more at the convection portion of the reformer according to the conventional method, hydrocarbons of C2 (ethane) or more of the natural gas are caused to thermally decompose, thereby generating carbon. The carbon thus generated tends to adhere onto the inner wall of the natural gas-preheating portion (pipeline) to thereby deteriorate the heat exchanging performance of the pipeline and hence deteriorating heat exchanging rate.
Further, if the surface temperature of the preheating portion is raised higher, the preheating portion may be possibly damaged. Additionally, if the carbon thus generated is allowed to inter into the catalyst layer incorporated in the reaction tube of reformer and located on a downstream side of the preheating portion, the catalyst layer may be clogged, thereby badly affecting the reaction and heat transfer, or under some circumstances, the catalyst as well as the reaction tube may be possibly damaged.
Therefore, in order to avoid a wasteful consumption of natural gas on the occasion of preheating a natural gas incorporated with steam and carbon dioxide at the convection portion of the reformer, it is required in the conventional manufacture method of synthesis gas to control the preheating temperature to less than 560xc2x0 C. As a result, it is difficult according to the conventional method to reduce the fuel consumption of the reformer and to effectively carry out the recovery of heat at the convection portion.
Therefore, an object of this invention is to provide a method for manufacturing a synthesis gas, which makes it possible to feed a natural gas incorporated with steam and carbon dioxide and preheated to a relatively high temperature to a reformer, thereby making it possible to save the fuel consumption of the reformer and to effectively utilize the waste heat of the reformer.
Namely, this invention provides a method of manufacturing a synthesis gas by using a synthesis plant comprising a reformer having a steam reforming reaction tube, a combustion radiation portion provided around the reaction tube, for heating the reaction tube by combusting fuel, and a convection portion communicating the combustion radiation portion, the method comprising the steps of;
adding steam to a natural gas to prepare a stream-containing natural gas;
passing the stream-containing natural gas through the convection portion of the reformer, thereby preheating the stream-containing natural gas;
preheating carbon dioxide by passing the carbon dioxide through the convection portion of the reformer; and
feeding the stream-containing natural gas preheated and the carbon dioxide preheated to the reaction tube, thereby producing a synthesis gas containing hydrogen and carbon monoxide.
This invention further provides a method of manufacturing a synthesis gas by using a synthesis plant comprising a reformer and a preliminary reformer which is provided on the upstream side of the reformer, the reformer comprising a steam reforming reaction tube, a combustion radiation portion provided around the reaction tube, for heating the reaction tube by combusting fuel, and a convection portion communicating the combustion radiation portion, and the method comprising the steps of;
adding steam to a natural gas to prepare a stream-containing natural gas;
passing the stream-containing natural gas through the convection portion of the reformer, thereby preheating the stream-containing natural gas;
feeding the stream-containing natural gas preheated via the preliminary reformer to the reaction tube;
preheating carbon dioxide by passing the carbon dioxide through the convection portion of the reformer; and
feeding the carbon dioxide preheated via a passageway, which is located between the reaction tube and the preliminary reformer and passed the stream-containing natural gas preheated, to the reaction tube, thereby producing a synthesis gas containing hydrogen and carbon monoxide.
This invention also provides a method of manufacturing a synthesis gas by using a synthesis plant comprising a reformer and a partial oxidation furnace which is provided on the downstream side of the reformer, the reformer comprising a steam reforming reaction tube, a combustion radiation portion provided around the reaction tube, for heating the reaction tube by combusting fuel, and a convection portion communicating the combustion radiation portion, and the method comprising the steps of;
adding steam to a natural gas to prepare a stream-containing natural gas;
passing the stream-containing natural gas through the convection portion of the reformer, thereby preheating the stream-containing natural gas;
preheating carbon dioxide by passing the carbon dioxide through the convection portion of the reformer;
feeding the stream-containing natural gas preheated and the carbon dioxide preheated to the reaction tube, thereby producing a synthesis gas containing hydrogen and carbon monoxide;
introducing the synthesis gas into the partial oxidation furnace; and
introducing gas containing oxygen into the partial oxidation furnace, thereby allowing a reaction to take place between the synthesis gas and the oxygen.
In each of the manufacturing methods of a synthesis gas described above, it would be possible to employ carbon dioxide that has been recovered from the combustion waste gas generated at the combustion radiation portion of the reformer.
It is also possible to employ the carbon dioxide recovered from the synthesis gas produced on a downstream side of the reformer.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.